Well, the title is self-explaining so let's jump in the subject

A huge list of intersections calculating (very very useful for raytracers). There are several links for each intersection so even if there's a broken link, you should find what you want.
A complete radiosity tutorial (in french though).
You need textures ? I mean *good* textures ? Check this website !
An awesome tutorial about the HSV color space.
ALL formulas to convert color spaces (a huge list of different color spaces).
Relsoft's website's tutorials section (Heya rel

). You wanna code 3D software stuff ? Check it's 3D tutorials (Bottom of the page). And there are also a lot of very very cool tutorials.
An article about fog rendering. A must-read if you wanna add fog to your 3D engine !
A thesis of M. Daniel Vlasic about Fake Phong Shading. Contains a huge quantity of useful informations about general shading techniques too. A must-read !!
A small article about shading. Presents some ideas about light handling.
A short description of the OBJ file format. Useful if you wanna write your OBJ importer.
A very (VERY) complete description of the OBJ file format.
A reflexion about rendering engines.
A very short article about simplified Environment Mapping.
"This article presents, in two parts, a detailed implementation of refractive texture mapping for a simple water wave simulation using directional sine waves applied to a flat polygonal mesh."
Phong shading : "What I've tried to do is explain the factors of the phong lighting equation -- what parts do what, and why it works."
A very cool article about shadow volumes.
The shadows rendering home page ! A HUGE list of different resources about shadow rendering.
An article about the different shadow generation techniques.
VoilĂ
Final notes : Some of you may recognize some of those sites. I found some of those links here indeed. If you have some cool links about 3D/graphics coding you want to share, don't hesitate to post it here (but please use the same scheme : a list bracket for the link and a little description below for clarity)